In the fabrication of three dimensional integrated circuit assemblies, such as multi-chip modules, an interconnect layer is interposed between two layers of active circuitry to provide signal and power routing functions. As such, electrically conductive vias or feedthroughs are required to convey signal and power traces vertically between the two major surfaces of the interconnect layer.
For many applications, the interconnect layer is comprised of a relatively thin (approximately 10 micrometers to 50 micrometers) layer of silicon that is processed to form openings through the layer at locations where feedthroughs are required. During a subsequent metallization step, a suitable metal is deposited within the openings to provide an electrically conductive connection from one side of the layer of silicon to the other.
However, a problem is often encountered in obtaining a high quality, low resistance connection between the two surfaces. This problem is due in part to the conventional vertical-profile silicon trench etch process, such as a reactive ion etch, that is employed to form the feedthrough openings. The significant depth (typically in the range of 10-50 micrometers) through which the metallization must be deposited, in combination with the essentially vertical surfaces of the opening sidewalls, can result in variations in metal thickness and coverage within the openings. This leads to the formation of electrical connections that have less than optimum electrical resistance and reliability characteristics.
It is thus one object of this invention to provide a method for fabricating reliable, low resistance electrical feedthroughs within a semiconductor material.
It is a further object of this invention to provide a method for fabricating an electrical interconnect layer that is suitable for use in a multi-chip module, the electrical interconnect layer including low resistance and highly reliable feedthroughs.
It is one further object of this invention to provide a silicon electrical interconnect layer wherein feedthroughs have inwardly tapering sidewalls for improving the contact metal step coverage.